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Visual Perception Modeling: Local Operations, Histograms, Point Operations, and Algebraic Operations

Explore the different concepts in visual perception modeling, including local operations, histograms, point operations, and algebraic operations. Learn how these operations can be applied in various applications such as contrast enhancement, histogram matching, traffic estimation, and blue-screen editing.

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Visual Perception Modeling: Local Operations, Histograms, Point Operations, and Algebraic Operations

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  1. Outline • Announcements • Projects • Local operations • Histograms • Point operations • Algebraic operations • Applications • Image morphing

  2. Announcements • Projects • Based on my programs • Need to get familiar with my programs • Find the database you are interested in on the web • Change my program to get the system work • Tune parameters to improve performance • Based on a paper or your idea • Need to talk to me either this week or next week • Make sure that it is doable during the time framework • Report and in-class presentation Visual Perception Modeling

  3. Announcements • Research papers • Need to talk to me on the papers or the subjects you are interested in • Decide on the topics within two weeks • Write a research paper for each topic • Do a presentation in class for each topic Visual Perception Modeling

  4. Local Operations • A image can be represented by a matrix • Neighborhood • Local operations • Operations whose output depends only on pixels within a local neighborhood Visual Perception Modeling

  5. Neighborhoods • 4-neighborhood • For pixel (i, j) {(i-1, j), (i+1, j), (i, j-1), (i, j+1)} • 8-neighborhood • For pixel (i, j) {(i-1, j), (i+1, j), (i, j-1), (i, j+1) (i-1, j-1), (i+1, j+1), (i+1, j-1), (i-1, j+1)} Visual Perception Modeling

  6. Point Operations • A point operation takes a single input image into a single output image in such a way that each output’s pixel value depends only upon the pixel value of the corresponding input pixel • Contrast enhancement • Contrast stretching Visual Perception Modeling

  7. Types of Point Operations • Linear point operations • PO = f(PI) = a PI + b • Nonlinear point operations • PO = f(PI) where f is a nonlinear function Visual Perception Modeling

  8. Image Histograms • Histogram • The histogram is the function showing, for each possible value, the number of pixels in the image that have that particular value Visual Perception Modeling

  9. Multi-dimensional Histograms • A multi-dimensional histogram is a function of several variables • For a color image, we can have a three-dimensional histogram Visual Perception Modeling

  10. Point Operations and Histograms • Point operations modifies the histogram in a predictable way Visual Perception Modeling

  11. Applications of Point Operations • Histogram equalization • Find a point operation such that the histogram of the resulting image will be a flat histogram • Histogram matching • Find a point operation such that the histogram of the resulting image will match the one of a given image Visual Perception Modeling

  12. Algebraic Operations • Algebraic operations are operations that produce an output image which is the pixel-by-pixel sum, difference, product, quotient, or other forms of functions of two input images Visual Perception Modeling

  13. Traffic Estimation • Suppose aerial photographs are taken of highway section • To estimate how many cars are there in the section, find the difference between two consecutive images and count the number of white regions Visual Perception Modeling

  14. Blue-Screen Editing Visual Perception Modeling

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